Electroluminescent generator



Jan. 12, 1965 M. SOLOW ETAL 3,165,631

ELECTROLUMINESCENT GENERATOR Filed July 26, 1960 2 Sheets-Sheet 2 9 2 f. 8 eeeeeeeeeeeeeeeeeeee a hhhhhhh ti 3,165,631 Patented Jan. 12., 1965 3 165,631 ELECTROLUMIblESC NT GENERATOR Max Solow, Silver Spring, Md, Nathaniel L. Colehuru, Washington, D.C., and Raymond C. Wiley, Rockvllle, Md., assignors to the United States of America as represented by the Secretary of the Navy Filed July 26, 1960, Ser. No. 45,509 3 Claims. (Cl. 250-84) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein maybe manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates generally to the field of solid state physics and is more particularly concerned with a method and a device for generating a short intense pulse of light or a burst of electrons.

This invention utilizes properties of certain metal oxides which contain F centers. The F center is a peculiar type of defect in the crystal lattice characterized by the fact that a metal atom is missing from its position in the crystal lattice. In place of the missing atom is found an electron pair. The oxides of the following metals are known to contain these F centers: aluminum, zinc, magnesium, cadmium, indium and gallium.

This invention also utilizes a phenomenon known as the electro-acoustic or the acoustic-electric eifect. That is, the phenomenon when a shock wave passes through a material, [generally a metal or a semiconductor although in some cases the effect has been observed in insulators] it sweeps before it a sheet of electrons. The electrons are, in the case of a metal, probably conduction electrons.

It is an object of this invention to provide a method for the generation of a pulse of light which is intense and 3 yet of sufiiciently short duration for use in ultra high speed photography. I

Another object of this invention is to provide a solid state device which acts as a convenient source of electrons.

Another object is the provision of a novel high intensity light source of short duration which is rugged and durable.

Another object is the provision of a new and improved light and electron generator.

These and many other objects will become more readily apparent to those skilled in the art when the following specification is read and considered along with the attendant drawings wherein like numerals designate like or similar partsthroughout the several views and in which:

FIG. 1 is a view, partly schematic, which indicates one preferred embodiment of the invention;

FIG. 2 is a diagrammatic representation of 'a crosssection of the F center forming metal oxide of FIG. 1;

FIG. 3 is a diagrammatic representation of the oxide of FIG. 2 showing the material as a shock wave sweeps through it;

FIG. 4 indicates a cross-section of the oxide of FIG. 2 as the shock wave reaches the free surface; and

FIG. 5 indicates the oxide of FIG. 2 as the electrons begin leaving the free surface of the oxide.

Referring now to FIG. 1, a generator is composed of a thick porous layer of metal oxide 11. As stated hereinbefore, the metal oxide may be the oxide of any available F forming metal such as aluminum oxide, zinc oxide, magnmium oxide, cadmium oxide, indium oxide or gallium oxide. At once surface of the oxide layer is bonded a sheet or block of metal 12. The composition of this layer 12 is not critical, for the sake of convenience, however, it may be desirable to utilize a metal whose oxides are known to form F centers and to oxidize one surface of this metal to chemically form the oxide layer 11, Thus, if aluminum is utilized as the metal 12 the surface may be treated with an acid such as phosphoric or nitric in order to produce a thick porous coating of oxide. I

explosive material 13, which may be any high explosive, abuts the surface of metal 12 opposite from the oxide layer 11. A typical generator may employ the explosive known as compositionB which is a mixture of RDX, TNT withsmallamounts of Wax and. polyisoluctylene. A plane Wave generator shown schematic allyv at 14 is employed to generate a planar detonation wave to initiate the explosive 13 thereby to impinge the metal 12 and the oxide 11 with a planar shock wave. These planewave generators may conveniently be an air lens, as is well known to those skilled in the art.

collar 15 is secured to the free surface 28 of oxide 11, while a light transmitting plate 16 is fixed to the opposite endof thecollar 15 thereby providing a closed space adjacent to the free surface ofthe oxide, which space may be evacuated inorder to increase the efficiency of operation of the device. v Asource of actinic radiation 17 is placed some distance from the oxide layer 11. This source of radiation may conveniently be a radioactive material light source, an electron source, or a source of X-rays. For convenience, alight source may be employed as the source 17. As shown inthe figure, the beam 19 from the source 17 impinges upon a half-silvered mirror 18 and part of it is directed upwardly asshown at-21 and discarded. The remainder 22 impinges on the surface 28 of the oxide. The light beam impinging on layer llserves to activate the layer preparatory to the passage of the explosive Wave through the oxide.- Each oxide is characterized'by a particular activation energy, that is, the energy required to liberate an electron from the F' centers. Thus, for aluminum this. energy is .--2.64 electron volts. Accordingly, if the layer 11 is aluminum oxide, it may be desirable that the light employed to illuminate its surface and activate or trigger it, be in the neighborhood of 4700 A. and may be in the'rangefrom about 4500 A. to 5500 A.

The light generated by the apparatus is emitted from the'free surface 28 of the oxide layer 11 as a light beam 23 which is directed by mirror 18 as beam 24 to a device 25 for utilizing the-light. This device may conveniently be a camera or a strip of film.

In the event that it is desired to utilize'the electrons generated by this device rather than the light, a grid 26 may be positioned at or near the free surface of layer 11 in order to control or'direct the beam of electrons toward a suitable target [not shown].

The operation of this device may be readily understood by referring to FIGS. 2', 3, 4 and 5. The theory of operation, while it is believed to be accurate, is advanced only as one possible explanation of the device.

As shown in FIG. 2, the oxide layer contains a plurality of F centers. At the free surface of this oxide layer, a layer 27 of oxygen atoms is adsorbed. The atoms in this layer 27 contain one negative charge, that is, they contain a surplus electron. The triggering radiation, bearing the notation H11, does one of two things as it impinges upon the surface of oxide 11. Either it impinges upon an adsorbed oxygen atom or it penetrates slightly into the oxide layer. If the radiation impinging upon the adsorbed oxygen atom has sufiicient energy it excites the excess electron in the adsorbed oxygen and the electron is emitted. The neutralized oxygen atom combines with a neighboring charged atom to form a molecule of oxygen gas and to give off a second electron. The electrons emitted by this process may move either into the space surrounding the free surface 28 of the oxide layer 11 the observed operation of or they may be directed into the oxide layer. Those electrons that are directed into the oxide may impinge upon an F center. The electrons trapped at the F centers behave similarly to atomic electrons and may be thought of as moving about the Fv center in Bohr orbits. If the impinging electron from the oxygen atoms contains sufficient energy, it may knock out one of these electrons thereby forming an F center which is similar to. an F center but contains only one electron. In a material which customarily contains F centers, this F center may be thought of as an electron trap since an electron moving through the material would tend to be attracted. to the effective positive charge of the F center and be captured to reform an F center.

Some of the triggering radiation bypasses the adsorbed oxygen atom layer or impinges upon the surface after the oxygen layer has been substantially removed by the process described and may penetrate into the oxide surface. The depth of penetration may be enhanced by the fact that the oxide surface is made thick and porous by the action of the acid etch.

If the radiation contains the proper amount of energy, it may excite one of the electrons in the F center upon which it impinges. The F' center ionizes to emit an electron Which may then travel freely throughout the oxide layer ultimately to be captured by another F center. After a time, the number of F centers which are ionized to form F centers reaches an equilibrium With the number of F centers which recapture electrons wandering through the oxide and reform an F center. When this equilibrium condition is reached, the number of F centers in the oxide layer is at a maximum. This process has been found to take place in less than one microsecond.

Referring now to FIG. 3 which indicates the phenomenon taking place as a shock wave 29 moves through the oxide sweeping before it a sheet of electrons 31. This sheet of electrons is generated in the metal plate or sheet 12, FIG. '2, as the shock wave sweeps through the metal driving the metals conduction electrons before it. A few electrons may be stripped from the oxide layer but the metal serves as the main supply of electrons for this electron sheet 31. oxide 11, the newly formed F'centers are quickly reconverted into F centers with the attendant emission of a quantum of light [in the 4700 A. range for the caseof aluminum oxide centers] When the shock wave reaches a free surface of the oxide 11 as shown in FIG. 4, a brilliant burst of light energy is given off as the reformation of F centers from F centers takes place rapidly near the surface. This burst of lightmay be employed to illumimate a specimen which is to be photographed by ultrahigh speed techniques, for example, a shock wave.

All the electrons in the sheet are not utilized in the reformation of F centers. Many are available at the surface for emissioninto the surrounding medium as shown in FIG. 5. The Auger effect may account for this electron burst.

It should therefore be apparentthat by this invention is.

As the electron sheet passes through the Having thus described this invention with reference to but one preferred embodiment, it is to be understood that it is by no means limited but is susceptible to many alterations and modifications without departing from the spirit or scope thereof. Accordingly, the foregoing illustrative example should not be construed as limiting this invention inany manner, rather the scope of the appended claims only define the invention.

What is claimed is:

l. A device for the production of short intense pulses of energy which comprises (1) an oxide layer having a free surface (2) a metal sheet bonded to a surface of said oxide layer opposite the free surface of said oxide layer, said metal being selected from the group consisting of aluminum, zinc, magnesium, cadmium, indium and gallium (3) explosive means contiguous with said metal sheet (4) radiation means directing energy upon said oxide layer and thereby activating said oxide layer (5) means for generating a planar shock wave by initiation of said explosive means whereby said planar shock wave impinges said metal sheet and said oxide layer and a brief pulse of energy is emitted from the free surface of said oxide layer.

2. A device for the production of short intense pulses.

of energy which comprises (1) a metal body having an oxidized surface, said metal being selected from the group consisting of aluminum, zinc, magnesium, cadmium, indium and gallium (2) explosive means contiguous with said metal body (3) radiation means directing energy upon said oxidized surface and thereby activating said oxidized surface V (4) means for generating a planar shock wave by initiation of said explosive means whereby said planar shock wave impinges said metal body and said, oxidized surface and a brief pulse of energy is emitted from the oxidizedsurface.

3. A method of generating an intense pulse of energy which comprises (l) exposing a metallic body having an oxidized surface to actinic radiation in order to activate said oxidized surface, the, metal in said body being selected from the group consisting of aluminum, zinc, magnesium, cadmium, indium, and gallium and (2) shocking said body on a surface thereof opposite said oxidized surface by means of an explosively initiated planar shock wave.

References Cited by the Examiner UNITED STATES PATENTS 2,449,880 9/48 Cox 313-109 2,923,852 2/60 Scott 315lll 3,093,735 6/63 Blakewood 250-83 RALPH G. NILSON, Primary Examiner.

GEORGE N. WESTBY, Examiner. 

1. A DEVICE FOR THE PRODUCTION OF SHORT INTENSE PULSES OF ENERGY WHICH COMPRISES (1) AN OXIDE LAYER HAVING A FREE SURFACE (2) A METAL SHEET BONDED TO A SURFACE OF SAID OXIDE LAYER OPPOSITE THE FREE SURFACE OF SAID OXIDE LAYER, SAID METAL BEING SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, ZINC, MAGNESXIUM, CADMIUM, INDIUM AND GALLIUM (3) EXPLOSIVE MEANS CONTIGUOUS WITH SAID METAL SHEET (4) RADIATION MEANS DIRECTING ENERGY UPON SAID OXIDE LAYER AND THEREBY ACTIVATING SAID OXIDE LAYER (5) MEANS FOR GENERATING A PLANAR SHOCK WAVE BY INITIATION OF SAID EXPOLSIVE MEANS WHEREBY SAID PLANAR SHOCK WAVE IMPINGES SAID METAL SHEET AND SAID OXIDE LAYER AND A BRIEF PULSE OF ENERGY IS EMITTED FROM THE FREE SURFACE OF SAID OXIDE LAYER. 